In recent years, the use of cellular communication systems having mobile terminals which communicate with a hardwired network, such as a local area network (LAN) and a wide area network (WAN), has become widespread. Retail stores and warehouses, for example, may use cellular communications systems to track inventory and replenish stock. The transportation industry may use such systems at large outdoor storage facilities to keep an accurate account of incoming and outgoing shipments. In manufacturing facilities, such systems are useful for tracking parts, completed products and defects.
A typical cellular communication system includes a number of fixed base stations or access points interconnected by a system backbone. Also included in many cellular communication systems are intermediate base stations which are not directly connected to the system backbone. Intermediate base stations, often referred to as wireless base stations or repeaters, increase the area within which base stations connected to the system backbone can communicate with mobile terminals.
Associated with each base station is a geographic cell. A cell is a geographic area in which a base station has sufficient signal strength to transmit and receive data from a mobile terminal or other device with an acceptable error rate. Typically, base stations will be positioned along the backbone such that the combined cell area coverage from each base station provides full coverage of a building or site. Further, it is also typical to have the cell area of coverage from two or more base stations to overlap or be co-located.
Wireless communication systems such as those described above require that a base station and a mobile terminal communicate on the same frequency channel in order to exchange information. Often times, the noise level on a particular channel may become excessive and therefore a base station, for example, will initiate a move to a different frequency channel where better system performance can be achieved. Prior to changing to a different frequency channel, however, the base station must go off-line from its current channel to search for other channel candidates and to evaluate the current noise conditions of those channels. Unfortunately, by going off-line the base station can no longer communicate with other devices on what had been the current channel utilized by the base station. As a result, communications between the base station and any mobile terminals registered thereto are suspended so as to reduce overall system performance.
As an example, in a known frequency agile direct sequence spread spectrum (DSSS) system a base station is able to select among a plurality (e.g., five) available channels on which to communicate. On occasion, the base station may determine that the noise conditions on the current channel are too high for reliable communications and therefore decide to move to a new channel among the available channels. In order to determine which channel to move to, the base station broadcasts a message to be received by all mobile terminals registered to the base station indicating that the base station will be going temporarily off-line. This avoids the possibility of a mobile terminal transmitting information to the base station during such a time when the base station is not configured to receive such information. The base station then utilizes its transceiver to scan communication conditions (e.g., noise conditions) on all other available channels.
Based on such analysis, the base station then determines whether it is desirable to change to a new channel which may offer improved communication conditions (e.g., lower noise conditions). If more favorable conditions are available on another channel, the base station then returns to the original channel and attempts to inform all mobile terminals to jump to the newly selected channel. Otherwise, the base station simply remains on the original channel and informs the mobile terminals that the base station is back on line.
There are, however, a number of drawbacks associated with such an approach for determining to which channel the base station should change, if at all. The requirement that the base station go off-line in order to search for other channels significantly reduces overall system performance. Additionally, the base station typically assesses the noise conditions on each of the other channels over a short period of time and often leads to skewed results when, for instance, noise conditions are high or low on a particular channel due to conditions which are only temporary. Similar difficulties also exist for mobile terminals which evaluate the noise conditions in order to initiate channel switching.
In view of the aforementioned shortcomings associated with conventional communication systems involving different channels on which the base stations and mobile terminals may communicate, there is a strong need in the art for a system and method for minimizing loss in system performance associated with devices initiating a change in communication channels. Further, there is a strong need in the art for a system and method of changing channels utilizing information which accounts for temporary fluctuations in the communication conditions on other channels.